Chapter 18, Problem 1CYR

Summary Introduction

To review:

Whether the following statements are true or false:

a. Arteries are the exchange vessels of the cardiovascular system.

b. The tunica intima is composed of a sheet of endothelium, connective tissue, and the internal elastic lamina.

c. The tunica media consists of smooth muscle cells innervated by vasomotor nerves.

d. Muscular arteries control blood flow at the tissue level.

e. Veins have smaller lumens, more elastic fibers, and more smooth muscles than arteries.

Introduction:

The cardiovascular system contains a billion blood vessels, which transport blood to tissues and so carry it back to the heart. It involves the exchange of gases, nutrients, and wastes. These blood vessels involve arteries, veins, and capillaries. They also regulate blood flow to tissues and control blood pressure.

Explanation of Solution

a. The statement “Arteries are the exchange vessels of the cardiovascular system” is false. The arteries carry blood away from the heart and supply blood to the various organs and tissues. The pulmonary artery carries the deoxygenated blood and the systemic artery carries oxygenated blood. The exchange vessels of the cardiovascular system are capillaries. So, the correct statement would be “Arteries are distribution system of the cardiovascular system.”

b. The statement “The tunica intima is composed of a sheet of endothelium, connective tissues, and the internal elastic lamina” is true. Tunica intima is the innermost layer of the blood vessels. Endothelium provides a smooth surface for blood flow. Deep in the endothelium, the internal elastic lamina is present, which consists of a thin layer of subendothelial connective tissues and a layer of elastic fibers. This layer has the ability to restore the original shape of the blood vessels after stretching.

c. The statement “The tunica media consists of smooth muscle cells innervated by vasomotor nerves” is true. Tunica media is the middle layer of the blood vessel wall. It consists of two components—a layer of smooth muscle cells and a layer of elastic fibers called the external elastic lamina. The smooth muscles of tunica media are supplied with nerves from a sympathetic nervous system called the vasomotor nerves. These nerves enable the action of vasodilation and vasoconstriction of blood vessels.

d. The statement “Muscular arteries control blood flow at the tissue level” is false. Muscular arteries contain well-developed tunica media, which consist of smooth muscle cells. Due to the presence of smooth muscle cells, muscular arteries can change their diameter with vasoconstriction and vasodilation. This helps in the regulating the blood flow to different organs. So, the correct statement would be “Muscular arteries control the blood flow at the organ level.”

e. The statement “Veins have smaller lumens, more elastic fibers, and more smooth muscles than arteries” is false. Veins act as the blood reservoirs of the body. Blood can be diverted from veins to other parts of the body when needed. The arteries are circular, whereas veins appear collapsed, so they have much thinner walls. The correct statement is “Veins have fewer elastic fibers, less smooth muscles, and a larger lumen that arteries.”

Conclusion

Thus, it can be concluded that the statements (b) and (c) are true and the statements (a), (d), and (e) are false.